a) Field of the Invention
This invention relates to a smelt spout for delivering smelt from a chemical recovery furnace or boiler, and to a delivery system incorporating one or more such spouts.
b) Description of the Prior Art
In the kraft pulping process concentrated used liquor (black liquor) is fed into a recovery furnace wherein the remainder of the water is evaporated and a char composed primarily of sodium sulphate, sodium carbonate and some organic is formed. This char falls to the hearth bed of the furnace which is maintained under reducing conditions and at high temperature to form a smelt consisting essentially of molten sodium sulphide and some sodium sulphate. The hot smelt produced in the recovery furnace pours out of the furnace in a continuous stream on the smelt spout and discharges therefrom into a tank containing an aqueous solution in which it is dissolved. After it leaves the spout, and before it hits the surface of the liquid in the tank, the smelt is broken up into smaller particles by being impinged with a jet of steam or the like.
The service conditions imposed on the smelt spout are extremely severe. Smelt is corrosive and flows at a temperature in the range of 1400.degree. F. to 1700.degree. F. Conventionally, smelt spouts made of metal have been internally cooled by cooling water at a specific flow and temperature. While water cooling prolongs smelt spout life, it also presents a potential safety hazard, since it is a source of water that, in the event of a leak, could cause serious problems. Contact between water in any appreciable quantity and the molten smelt in the chemical recovery boiler bed can result in a violent physical reaction and explosion.
In order to overcome this hazard, non-water cooled smelt spouts have been proposed. U.S. Pat. No. 4,011,047 Tremblay which issued Mar. 8, 1977 describes a smelt spout which is a composite of an outer metal plate covered by a layer of insulating brick and which in turn is covered by a layer of plastic refractory material. This composite spout obviously is quite massive and mounting it can be difficult particularly when one considers that the spout must be supported in a cantilevered fashion from the furnace wall. The Tremblay spout structure also has a barrier end wall damming up and retaining on the spout a certain amount of molten smelt, thus adding to the weight of the spout that must be supported.